A magneto-resistive random access memory is a kind of non-volatile memory device, which possesses an advantage of comparable speed in data read/write regarding to a static random access memory. Its storage density is also similar to that of a static random access memory. One more attractive feature of a magneto-resistive random access memory is that it is almost free of reliability problem caused by the deterioration of device. It is called a versatile memory for its various advantages and it is capable of fully replacing the current applications of the static/dynamic random access memory and the flash memory.
It is different from the principle of a static/dynamic random access memory or a flash memory that a magneto-resistive random access memory stores information by a magnetic storage structure instead of the holding and releasing charges.
As shown in FIG. 1, a magnetic storage structure consists of two ferromagnetic plate electrodes, which are separated by a layer of insulating film. The “sandwich” structure is called a magnetic channel junction. Concerning the two magnetic electrodes in the magnetic channel junction, one electrode which is of a fixed magnetic field direction is called a fixed layer and the other electrode whose magnetic field direction changes with the external magnetic field is called a changeable layer. When the magnetic field direction of the changeable layer is as same as the fixed layer, the resistance of the entire magnetic channel junction becomes very small and the current flowing through the magnetic channel junction will be very large under the effect of an applied voltage. When the magnetic field direction of changeable layer is opposite to the direction of the fixed layer, the resistance of the entire magnetic channel junction becomes very large and the current flowing through the magnetic channel junction current will be very small under the effect of an applied voltage. The signal identification can be achieved by observing the change of current.
As shown in FIG. 2, the three-dimensional structures of two common magnetic channel junctions are introduced. The structure in the left part of the figure is a flat square structure and the right part of the figure shows an annular structure. In comparison with the magnetic channel junction with a flat square structure, the magnetic channel junction with an annular structure has a better access feature and it has become a consistently applied structure in the current semiconductor industry. However, in the manufacture, the process of the magnetic channel junction with an annular structure is more complicated and the manufacturing cost will be higher. A magnetic channel junction with an annular structure has two diameters, for the inner side and the outer side. As the diameter of the inner side is usually very small, high resolution will be required for the exposure apparatus in the manufacturing process. However, the adoption of advanced exposure apparatus will increase the manufacturing cost significantly. Currently, it is a popular topic on how to manufacture an annular magnetic channel junction which has precise dimensions under the condition that the high-resolution exposure apparatus is not used.
Chinese patent (CN 1495929A) has disclosed a method of manufacturing a magneto-resistive memory. In the method disclosed, a multilayer film is formed by sequentially forming a titanium layer, a titanium nitride layer and an aluminum layer on an insulating film. Then a photo mask pattern is formed. An annular magnetic layer is formed by etching with boron trichloride as reaction gas. The annular structure in the patent is formed by one-time photoetching and one-time etching, so the exposure apparatus in the manufacturing process is with high resolution ratio requirement.
Chinese patent (CN 102867913A) has disclosed a method of forming an annular storage unit of a magneto-resistive memory. Firstly, the periphery of a cylinder structure polysilicon is metalized by a metallic silicide process. Secondly, the polysilicon on the inner side of the metal silicide is removed to get an annular hard mask of metal silicide. Finally, the hard mask is used to etch the thin film layer of the magnetic channel junction to get an annular storage unit with precise dimensions which is applied to a magnetic memory. The patent provides a method of manufacturing an annular magnetic channel junction with precious dimensions without high-resolution exposure apparatus.